Method of manufacturing abrasive articles



V is used to attach the grains to the backing com-- Patented Feb. 23,1937 UNITED STATES METHOD OF PATENT OFFICE MANUFACTURING ABRAS ARTICLESOsborne L. Mahlman, Kenmore, N. Y., assignor, by mesne assignments, toThe Carborundum Company, Niagara Falls, N. Y., a .corporation ofDelaware No Drawing.' Application May 19, 1936 Serial No. 80,578 j 8Claims.

This invention relates to a method of manufacturing abrasive coatedarticles wherein abrasive grains are attached in'a substantially singlelayer to a backing. 'More particularly the invention is concerned withamethod of manufacturing abrasive coated products wherein the adhesivewhich prises essentially a heat-hardenable. resin.

.In a copending application Serial No; 693,395,

filed October 12, 1933, there is described a method of making abrasivecoated products wherein a 1 backing material is first coated with aheat- The thus prepared article is heated to soften the hardenableresinousliquid; such. as a normally liquid heat-hardenable phenoliccondensation product. A loose mass of abrasive grains individuallycoated with a heat-hardenable resin is prepared and applied to theliquid coated backing.

resinous coating on the abrasive grains, hardening the liquid coating onthe backing, and causing a welding between the resin coatingson thegrains and the hardened liquid on the backing whereby the grains arefirmly attached to the backing. This method has been found satisfac toryfor a. number of purposes. It has been found, however, that when thismethod is employed the resin coatings on the grains, which completelysurround and enclose the grains, tend to remain in place about thegrains. As a consequence the welding between. the resin coatings on thegrains and the liquid on the backing occurs only at the juncture of thegrain and the liquid and a substantial part of the resin on the grainsremains about the outer or grinding surfaces of the grains. Thisdetracts somewhat from the value of the article because the sharp andhard surfaces of the grains areat least temporarily covered up by theresin coatings which must be removed in use before the grains areexposed, and furthermore this resin is of no value in attaching thegrains to the backing and is therefore wasted so far as any use as abinder is concerned.

It is an object of this invention to provide a method which willovercome these objections.

Another object is to provide a method for manu-.

facturing coated abrasive articles containing a resinous binder forattaching abrasive grains "to a backing which will utilize substantiallyall of the resinous material for binding the grains to the backing,Still another object of the invention is to provide a method for makingabrasive coated products wherein the abrasive grains are firmly attachedto a backing by a heat-hardened resin and the outer or grindingsurfacesof the grains are substantially free from resinous material.

.An understanding of my invention will be facilitated by a briefdiscussion of resins and their mode of reaction. In considering thisdiscussion,

it is to be understood that the particularmaterials and reactionsdiscussed are referredto by way of example and that the invention is notlimited to the particular materials here discussed,

but may be practicedbroadly as defined in the claims. I

It is well known that when a phenol and methylene body, such asformaldehyde, para-'- formaldehyde, hexamethylenetetramine, or. otheraldehydes such as furfural orbenzaldehyde are heated together instoichiometric proportions, there isfirst formed an oily liquid whichupon continued heating becomes solid. The solid.-

initially formed is fusible and soluble in such.

common solvents as alcohol and acetone andupon continued heating isgradually converted through the so-called B stage where the resinsoftens when heated but does not fuse and finally reaches peatedlyheated and cooled without effecting fur-' ther reaction to the B stageor C stage.

These permanently fusible products are commonly made and are spoken ofin the literature as Novolaks. Where they contain an excess of phenolthey may be made heat reactive by adding a methylene body. In carryingout my invention.

I take advantage of these properties of resins by v coating abrasivegrains with a permanently fusible type of resin as described above andcoating a backing with a liquid containing the reactive ingredient whichis deficient in the coating on the grains. For example, I may coat thegrains with the Novolak, which is permanently fu'siblebecause itcontains an excess of a phenol, and supply the methylene body which isrequired to make the Novolak heat reactive in the liquid material whichis put on the backing.- The converse method may also be used bysupplying "the excess of methylene body in the coating on the grains andusing a liquid containing an excess of a phenol.

Having applied a coating of resin coated grains to the liquid coatedbacking, I beat the article so prepared whereuponthe resin'coatingsbinder thus formed is converted to the infusible,

on the abrasive grains, being readily fusible, melt mixture thus formedof liquid on the backing with the originally solid resin on the grainscontains reactive proportions of phenol and methylene bodies and uponcontinued heatingthe insoluble condition. At the same time the outersurfaces of the abrasive grains, which are exposed above the layer ofbinder, are substantially -free from resin and are in the best conditionfor abrading. My method therefore provides an article containingabrasive grains attached to a backing by a heat-hardened resinousproduct, the outer surfaces of the grains being substantially free fromresinous binder.

In comparison with the articles made by the method wherein the usualheat-hardenable resin is applied to the grains, my articles are sharper.My method also utilizes all of the resinous material to bind the grainsto the backing. This is not true of the methods heretofore used becausearticles produced by those methods contain a substantial quantity ofresin on the tops of the abrasive grains. This distinction appliesequally to articles made by the use of grains coated with aheat-hardenable resin as described above and to articles prepared by theconventional method of first coating a backing with a liquid adhesive,applying a coating of grains, and then applying a second or sizingcoating of liquid adhesive over the grains.

My invention is adapted to be carried out by any of the usual coatingmethods. For example, a traveling web of a backing material may becoated by passing a Web over a rotating roller immersed in a vat ofadhesive and then distributing the coated grains onto the liquid coatedbacking as by feeding them from a hopper in ya. conventional manner.Where abrasive disks are to be manufactured, the use of which involvesonly a ring or band of abrasive extending inward from the periphery ofthe disk, the invention may be practiced by first stamping out disks ofbacking material, coating a ring or band of suitable width with a liquidadhesive, adding the coated grains, removing any excess grain as byinverting the article, and then heating the article to cause the resincoatings on the grains to flow onto the backing and to cause reaction ofthe binder whereby it is heat-hardened and the grains are adhesivelyattached to the backing.

The coatings on the abrasive grains may be applied in any conventionalmanner. Since I utilize a resin which is permanently fusible and whichdoes not harden upon heating, a convenient method for coating the grainsconsists in merely melting up the resin, which may be in lump form, andstirring the grains through it to distribute it over the surfaces of thegrains. The mixture may be continually agitated while it is being curedso as to prevent agglomeration of the grains, or the mass may be coatedwithout agitation and subsequently broken up to obtain ,a loose mass ofsubstantially individual grains.

Alternatively the resin which is to be put on 'the grains may first bepulverized and. the grains expensive operation, and makes it possible tocoat the grain with resin of known composition unadulterated by liquidwetting agents.

As will appear from a consideration of my improved method, my inventionhas a number of advantages over the methods heretofore used. As juststated, the invention makes it possible to employ lump resin which isconsiderably cheaper than finely pulverized resin. In comparison withthe older methods where liquid adhesives only are used, my inventiondispenses with one of the steps of coating with a liquid. Since it iscustomary to heat treat articles after the grain has been applied andbefore the second or sizing coating of liquid has been added, theelimination of this sizing coat dispenses with a heating operation aswell as with a coating operation. Furthermore the method providesarticles which are sharper and free cutting from the start, whereas thearticles of the prior art require a preliminary run to remove the resinfrom the top of the grains before the grains themselves are exposed. Mymethod also effects a saving in resin because the resin which is appliedis all utilized for attaching the grains to the backing. This is nottrue of the methods heretofore used.

The invention is adapted to a number of modifications such as theinclusion of inert fillers in the liquid coating. Any suitable backingmay be employed, such as paper, cloth, flexible steel, or for thatmatter, non-flexible backings such as thick steel or wood. The liquidcoating may be a solution of a heat-hardenable resin in a suitablesolvent or it may be a normally liquid resin to which is added eitherthe phenol or methylene body depending upon which is required to reactwith the resin applied to the grains.

I claim:

1. The method of making an abrasive coated article which comprisescoating abrasive grains with a solid permanently-fusible resin capableof becoming infusible by heating with a hardening agent, coating abacking with a heat-hardenable liquid resinous material containing ahardening agent for the permanently-fusible resin on the abrasivegrains, applying a layer of the coated grains to the resin coat on thebacking, and heating the coated backing to cause the resin on the grainsto flow into the liquid coating on the backing and to harden the resins.

2. The method of making an abrasive coated article which comprisescoating abrasive grains with a solid permanently-fusible phenolic resincapable of becoming infusible by heating with a hardening agent, coatinga backing with a heathardenable liquid resinous material comprising aphenolic condensation product and a hardening agent for thepermanently-fusible resin on the abrasive grains, applying a layer ofthe coated grains to the resin coat on the backing, and heating thecoated backing to cause the resin on the grains to flow into the liquidcoating on the backing and to harden the resins.

3. The method of making an abrasive goated article which comprisescoating abrasive grains with a solid permanently-fusible phenoliccondensation product resin containing excess phenol, coating a backingmaterial with a liquid containing a methylene body, applying asubstantially single layer of the resin coated grains to the liquid coaton the backing, and heating the article to cause the resin on the grainsto flow onto the backing and to cause reaction between the resin and theliquid, whereby the resin is heat-hardened and the grains are adhesivelyattached to the backing by the hardened resin.

4. The method of making an abrasive coated article which comprisescoating abrasive grains with a solid permanently-fusible phenoliccondensation product resin containing excess phenol, coating a backingmaterial with a heat-hardenable liquid comprising a phenoliccondensation product and a methylene body, applying a substantiallysingle layer of the resin coated grains to the liquid coated backing,and heating the article to cause the resin on thegrains to flow onto thebacking and to cause reaction between the resin and the liquid, wherebythe resin is heat-hardened and the grains are adhesively attached to thebacking by the hardened resin.

5. The method of making an abrasive coated article which comprisescoating abrasive grains with a solid permanently-fusible phenoliccondensation product resin containing excess phenol,

coating a backing material with a normally liquid heat-hardenablephenolic condensation product containing a methylene body, applying asubstantially single layer of the resin coated grains to the liquidcoated backing, and heating the article to cause the resin on the grainsto flow onto the backing and to cause reaction between the resin and theliquid, whereby the resin is heathardened and the grains are adhesivelyattached to the backing by the hardened resin.

6. The method of making an abrasive coated article which comprisescoating abrasive grains with a solid permanently-fusiblephenol-methylene condensation product resin containing excess methylene,coating a backing with a liquid containing free phenol, applying asubstantially single layer of the coated grains to the liquidcoatedbacking, and heating the article to cause the resin on the grains toflow onto the backing and heat-harden.

7. The method of making an abrasive coated article which comprisescoating abrasive grains with a solid permanently-fusiblephenol-methylene condensation product resin containing excess methylene,coating a backing with a heat-hardenable liquid comprising a phenoliccondensation product containing an excess of free phenol, applying asubstantially single layer of the coated grains to the-liquid coatedbacking,

and heating the article to cause the resin on the grains to flow ontothe backing and heat-harden.

8. The method of making an abrasive coated article which comprisescoating abrasive grains with a solid permanently-fusiblephenol-methylene condensation product resin pcontaining excessmethylene, coating a backing with a normally liquid phenoliccondensation product containing free phenol, applying a substantiallysingle layer of the coated grains to the liquidcoated backing, andheating the article to cause the resin on the grains to flow onto thebacking and heat-harden.

OSBORNE L. MAI-ILMAN.

